This invention relates generally to a control system for automatically controlling a work implement of an earthmoving machine and, more particularly, to a control system that controls the hydraulic cylinders of an earthmoving machine based on discrete values of output torque produced by the drive train of the earthmoving machine so as to ensure engine power is not diverted to the hydraulic system during times when greatest pile penetration capability is needed.
In general, earthmoving machines such as wheel loaders, excavators, track-type loaders, and the like are used for moving mass quantities of material. These earthmoving machines have work implements that can include a bucket. The bucket is controllably actuated by at least one hydraulic cylinder. The operator typically performs a sequence of distinct operations to capture, lift and dump material.
A typical work cycle for a loader can include an operator first positioning the bucket near the ground surface and close to a pile of material. The operator then directs the machine forward to engage the pile of material, subsequently lifting the bucket to generate a downward force on the machine to maintain traction while racking (tilting) the bucket back to capture the material. The operator then moves the earthmoving machine to a desired target location, e.g., dump truck, and dumps the captured material from the bucket. The operator then moves the earthmoving machine back to the pile of material to start this work cycle all over again.
U.S. Pat. No. 5,968,103 issued Oct. 19, 1999 to the present inventor, discloses a system and method for automatic bucket loading which controls the bucket tilt command in proportion to a sensed crowd factor. Crowd factors are sensed machine parameters, such as bucket force and driveline torque, which provide an indication of the degree to which the bucket of the machine is xe2x80x9ccrowdingxe2x80x9d the material. The efficiency with which the bucket captures material depends upon how effectively the machine penetrates the pile of material to fill the bucket before breaking free, while avoiding going so deep as to stall the machine or overload the ability of the hydraulic systems to break the bucket loose.
In the automated loading system disclosed in the Rocke ""103 patent, the control strategy typically proceeds immediately from lifting the bucket to racking, thereby diverting power to the hydraulic system during a time when more torque may be needed to penetrate the pile. When loading difficult materials, this diversion of power from the drive train can prevent the machine from fully engaging the pile, and result in only partially full bucket loads.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of this invention, a control system for automatically controlling a work implement of an earthmoving machine the work implement including a bucket, to capture, lift and dump material, the bucket being controllably actuated by a hydraulic tilt cylinder and at least one hydraulic lift cylinder is disclosed. The control system includes a torque indicating mechanism that provides a representative value for an amount of torque produced by the drive train of the earthmoving machine, an electronic controller for receiving the representative torque value from the torque indicating mechanism, generating a lift command signal responsive to sensed contact with the material to establish traction, terminating the lift command signal, determining when the representative value of torque received from the torque indicating mechanism exceeds a first predetermined value and then responsively generating a tilt command signal, and a hydraulic implement controller for controlling hydraulic fluid flow to the hydraulic cylinders in response to the command signals, wherein the predetermined value is selected so as to provide a delay between termination of the lift command signal and generation of the tilt command signal.
In another aspect of the present invention, a method for controlling a work implement of an earthmoving machine, the work implement including a bucket, to capture, lift and dump material, the bucket being controllably actuated by a hydraulic tilt cylinder and at least one hydraulic lift cylinder. The method includes the steps of providing a representative value of torque produced by the drive train of the earthmoving machine with a torque indicating mechanism, receiving the representative torque signal from the torque indicating mechanism, generating a lift command signal responsive to sensed contact with the material to establish traction, terminating the lift command signal, determining when the representative value of torque received from the torque indicating mechanism exceeds a first predetermined value and then responsively generating a tilt command signal with an electronic controller, and controlling hydraulic fluid flow to the hydraulic cylinders in response to the command signals.